Abstract

Vibronically resolved laser photoacoustic spectra of I2 vapor have been recorded at room temperature in the presence and absence of atmospheric air in the 490–680 nm (20402–14700 cm−1) region for what is, to our knowledge, the first time. The vibrational bands belong to the B3Π(Ou+) ← X1∑g+ transition, but the underlying continuum also results from the 1Π1u ← X1∑g+ and A3Π1u ← X1a∑g+ transitions. The mechanisms of photoacoustic signal generation are discussed by analyzing the photoacoustic intensity in light of Franck–Condon factors for the B ← X transition. Energy transfer to O2 caused by the photodissociation of I2 into 2P3/2 + 2P1/2 I atoms is observed in the presence of atmospheric air, and the predissociation of the B state has been observed for its vibrational levels v′ ~ 23–27.

Metrics

Table 1

Assignments of Vibronic Bands in the I2 Visible (B ← X) Photoacoustic Spectrum in the Presence of Air at Atmospheric Pressurea

Observed Band (cm−1)

Relative Photoacoustic Intensity (I1)

Assignment (v′, v″)

Calculated Band (cm−1)

Calculated Absorption Intensity (I2)

Relative Nonradiative Rate (I1/I2)

19 843

1.38

(56, 0)

19 843

0.597

2.31

19 821

1.40

(55, 0)

19 821

0.654

2.14

19 797

1.51

(54, 0)

19 798

0.715

2.11

19 773

1.58

(53, 0)

19 774

0.781

2.02

19 747

1.68

(52, 0)

19 748

0.852

1.97

19 719

1.79

(51, 0)

19 719

0.929

1.93

19 692

1.97

(50, 0)

19 690

1.011

1.95

19 660

2.10

(49, 0)

19 659

1.099

1.91

19 625

2.38

(48, 0)

19 626

1.194

1.99

19 591

2.61

(47, 0)

19 591

1.295

2.01

19 554

2.86

(46, 0)

19 555

1.402

2.04

19 516

3.16

(45, 0)

19 516

1.515

2.09

19 475

3.31

(44, 0)

19 476

1.635

2.03

19 433

3.67

(43, 0)

19 434

1.761

2.08

19 389

3.92

(42, 0)

19 389

1.891

2.07

19 340

4.14

(41, 0)

19 343

2.026

2.04

19 293

4.32

(40, 0)

19 295

2.165

2.00

19 242

4.51

(39, 0)

19 245

2.305

1.96

19 192

4.78

(38, 0)

19 192

2.445

1.95

19 137

5.01

(37, 0)

19 138

2.582

1.94

19 081

5.18

(36, 0)

19 081

2.714

1.91

19 021

5.22

(35, 0)

19 022

2.838

1.84

18 961

5.23

(34, 0)

18 962

2.951

1.77

18 897

5.25

(33, 0)

18 899

3.047

1.72

18 833

5.27

(32, 0)

18 834

3.125

1.69

18 767

5.25

(31, 0)

18 767

3.178

1.65

18 697

5.30

(30, 0)

18 698

3.204

1.65

18 625

5.17

(29, 0)

18 626

3.198

1.62

18 552

5.22

(28, 0)

18 553

3.158

1.65

18 477

5.23

(27, 0)

18 478

3.082

1.70

18 400

5.18

(26, 0)

18 400

2.968

1.75

18 338

3.37

(28, 1)

18 340

—

—

18 322

4.94

(25, 0)

18 321

2.818

1.75

18 264

3.10

(27, 1)

18 264

—

—

18 239

4.61

(24, 0)

18 239

2.635

1.75

18 187

3.20

(26, 1)

18 187

—

—

18 156

3.44

(23, 0)

18 156

2.421

1.42

17 978

2.02

(21, 0)

17 982

1.930

1.05

17 944

1.78

(23, 1)

17942

1.130

—

17 892

1.72

(20, 0)

17 892

1.660

1.04

17 860

1.58

(22, 1)

17 856

1.240

—

17 802

1.44

(19, 0)

17 801

1.400

1.03

17 772

1.43

(21, 1)

17 769

1.310

—

17 710

1.26

(18, 0)

17 708

1.150

1.10

17 683

1.41

(20, 1)

17 680

1.350

—

17 614

1.11

(17, 0)

17 613

0.920

1.21

17 591

1.27

(19, 1)

17 588

1.340

—

17 519

0.91

(16, 0)

17 516

0.710

—

17 498

1.13

(18, 1)

17 495

1.290

—

17 415

0.66

(15, 0)

17 417

0.532

—

17 400

0.97

(17, 1)

17 399

1.196

—

17 376

0.83

(19, 2)

17 376

0.283

—

17 315

—

(14, 0)

17 315

0.382

—

17 301

0.82

(16, 1)

17 302

1.067

—

17 283

0.78

(18, 2)

17 283

0.371

—

17 200

0.80

(15, 1)

17 203

0.914

—

17 186

0.77

(17, 2)

17 187

0.449

—

17 099

0.63

(14, 1)

17 103

0.749

—

17 089

0.72

(16, 2)

17 090

0.508

—

16 988

0.73

(15, 2)

16 991

0.538

—

16 887

0.60

(14, 2)

16 890

0.535

—

16 785

0.53

(13, 2)

16 787

0.500

—

16 679

0.50

(10, 1)

16 681

0.199

—

16 570

0.34

(9, 1)

16 571

0.122

—

16 460

0.26

(8, 1)

16 460

0.068

—

16 262

0.15

(12, 4)

16 263

0.036

—

16 245

0.15

(8, 2)

16 248

0.123

—

16 162

0.06

(11, 4)

16 157

0.058

—

16 150

0.11

(9, 3)

16 149

0.167

—

16 139

0.13

(7, 2)

16 135

0.071

—

16 051

0.70

(10, 4)

16 049

0.076

—

16 033

0.11

(8, 3)

16 037

0.127

—

16 023

0.11

(6, 2)

16 021

0.036

—

15 939

0.07

(9, 4)

15 939

0.084

—

15 924

0.09

(7, 3)

15 924

0.086

—

15824

0.08

(8, 4)

15 828

0.080

—

15 810

0.09

(6, 3)

15 810

0.051

—

15 712

0.07

(7, 4)

15 715

0.066

—

15 695

0.08

(5, 3)

15 694

0.026

—

15 618

0.06

(8, 5)

15 620

0.030

—

15 598

0.08

(6, 4)

15 600

0.047

—

15 502

0.06

(7, 5)

15 507

0.033

—

15 482

0.07

(5, 4)

15 484

0.029

—

15 390

0.06

(6, 5)

15 392

0.030

—

15369

0.06

(4, 4)

15 366

0.015

—

15 278

0.06

(5, 5)

15 276

0.022

—

15 181

0.06

(6, 6)

15 185

—

—

a Calculated band positions and the corresponding absorption intensities with molecular constants of I2 are given in the fourth and fifth columns, respectively. Nonradiative decay rates from vibrational levels v′ of the B state are given in the sixth column.